1. Field of the Invention
This invention relates to a method and apparatus for manufacturing a casting mold by gas-hardening casting sand.
2. Prior Art
To date various methods of manufacturing a casting mold by gas-hardening casting sand have been widely used. To reduce the amount of gas used, and to increase the resistance to the breakdown of a casting mold, a method of manufacturing a type of gas-hardened casting mold (the VRH method) is also well-known. This method is comprised of the steps of putting a casting mold, molded with gas-hardening sand, into a closed container; producing a vacuum in the container; and filling spaces between the particles of the casting sand in the casting mold with hardening gas to harden the casting mold to a given level of strength.
However, the conventional method has a problem in that the flowability of gas-hardening casting sand is inferior so that its packing density at the time of molding is relatively low. No attempt to increase the packing density to solve this problem was satisactory, but filling and compacting the mold takes a lot of time. In the carbon-dioxide mold method, among others, a reduction of time in packing the mold has been wanted, because the flowability of the casting sand is inferior due to the high coefficient of viscosity of water glass used as a caking additive, and because the packing is mostly done manually.
Considering above problems this invention has been made to provide a method and apparatus that can easily give a high packing density to sand for forming a gas-hardened casting mold and to increase the strength of the mold.